1. Field of the Invention
The present invention relates to a golf ball and more particularly to a golf ball having dimples of improved configurations formed on the surface thereof to make air in the periphery thereof turbulent during the flight thereof, so as to increase the flight distance thereof with a favorable aerodynamic symmetrical property maintained even though one great circle path unintersecting with dimples is formed on a seam line.
2. Description of the Prior Art
Normally, the golf ball has 280 to 540 dimples formed on the surface thereof. The role of the dimple is to reduce pressure resistance by shifting a separation point backward and improve lift by accelerating the difference between the above separation point and below the separation point. That is, in order to shift the separation point backward, it is necessary to make the flow of air in the periphery of the golf ball turbulent during the flight thereof to accelerate the transition of the turbulent flow of a boundary-layer and thereby cause the separation of the turbulent flow. Thus, it can be said that the dimple capable of making air in the periphery of the golf ball turbulent is aerodynamically superior.
In view of the role of the dimple, there are proposals of dimples, of the golf ball, having a function of making air in the periphery of the golf ball turbulent during the flight thereof. For example, the following golf balls were disclosed in Japanese Laid-Open Patent Publications: (1) a golf ball having large and small diameter dimples arranged thereon (Japanese Laid-Open Patent Publication No. 62-79072); (2) a golf ball having a plurality of kinds of dimples densely arranged thereon (Japanese Laid-Open Patent Publication No. 62-192181); (3) a golf ball having circular and uncircular dimples arranged thereon in combination with each other (Japanese Laid-Open Patent Publication No. 5-84328).
If a plurality of great circle paths unintersecting with dimples is formed on the surface of the golf ball, the area of a land, namely, the area of a region on which dimples are not formed, increases. As a result, the dimples are incapable of effectively making air flows turbulent. Thus, the present applicant proposed (disclosed in Japanese Laid-Open Patent Publication No. 04-150875) a dimple arrangement. According to the dimple arrangement, dimples formed in an orderly manner in divided regions formed by geometrically projecting a regular polyhedron on a spherical surface is varied such that great circle paths are not present on the surface of the golf ball except a great circle on a seam line, and dimples disposed on the seam line formed on a connecting surface of upper and lower mold are moved vertically or removed such that one great circle path is present on only the seam line.
When dimples with large and small diameter or dimples having circular and uncircular configurations are arranged on the surface of the golf ball densely and irregularly in combination with each other, such that one great circle path is present only on the seam line, air in the periphery of the golf ball can be made to be turbulent during the flight thereof and thus the flight distance thereof can be increased.
The golf ball having the above construction is, however, insufficient for maintaining a favorable aerodynamic symmetrical property because the great circle path unintersecting with dimples is present on the seam line. That is, the flight distances of the golf ball are different from each other depending on a hitting point thereof.
That is, the presence of a great circle path (S), unintersecting with dimples, formed on the seam line causes the flight distance of the golf ball in seam hitting to be different from the flight distance thereof in pole hitting. Seam hitting means a way of hitting a golf ball 1 such that a line connecting both poles (P) thereof serves as a rotational axis L1 in the back spin thereof, whereas pole hitting means a way of hitting the golf ball 1 such that a line perpendicular to the rotational axis L1 serves as a rotational axis L2 in the back spin thereof.
The golf ball causing the flight distances to be different from each other depending on a rotational axis is not recognized officially because the flight distances thereof are nonuniform.
It is important for the golf ball to have a favorable aerodynamic symmetrical property so that the difference between the flight distance thereof in seam hitting and the flight distance thereof in pole hitting is much less than the officially recognized standard distance.